S3, S4, R6, and reference classes. To be fair they are situational and not one size fits all. The stricter ones are mainly used in biostats where significant me

S3, S4, R6, and reference classes. To be fair they are situational and not one size fits all. The stricter ones are mainly used in biostats where significant metadata makes more sense in OO. S3 is nice and easy, primarily just a list with dispatches. Everything else is less so.